Many facilities, such as semiconductor clean rooms, typically require that significant quantities of outside make-up air be introduced into the facility to compensate for process air usage and leakage or to comply with code requirements. Such facilities often require that the relative humidity of the air within a building be controlled to a preselected target setting. A make-up air handler renders outside air that is necessary for use inside the plant to the conditions required to maintain control inside the plant. This typically requires temperature, humidity, and contamination control. Depending on outside air climatic conditions, this typically includes dehumidification by cooling of make-up air to extract undesirable moisture and may include air filtration when cleanliness of the inside environment is required: one conventional system for humidity control is described below in conjunction with FIG. 1.